<?php
class Youthor_Customer_Model_Entity_Address_Attribute_Source_Country extends Mage_Customer_Model_Entity_Address_Attribute_Source_Country
{
    public function getAllOptions()
    {
        if (!$this->_options) {
            $this->_options = Mage::getResourceModel('directory/country_collection')->addCountryIdFilter('CN')->toOptionArray(false);
        }

        return $this->_options;
    }
}